TCustomForm class

In unit Forms

The base type for TForm classes.

Declaration

pascal

TCustomForm = class(TCustomDesignControl)

Inheritance

Descends from it: TCustomDockForm TForm THintWindow TLazDockForm

Description

TCustomForm is a TCustomDesignControl descendant that implements the base type for TForm classes.

Forms represent a window or a dialog used as the user interface for a GUI application. It is a container where visual components (such as buttons, labels, edit fields, images, etc.) can be placed. It is also a designer surface which provides design-time support for configuration and layout of the content placed on the form.

TCustomForm acts an abstraction layer which masks implementation-specific routines required for the various widgetsets supported in the Lazarus Component Library ( LCL). Methods and properties are provided which interact with the underlying Operating System or platform, and provide a common API for form-related operations.

Properties

`ClientHandle`	protected	The Handle of the MDIForm client (container for MDI children).
`Active`	public	Indicates if the form is enabled, visible, and has focus.
`ActiveControl`	public	Gets or sets the active control on the form.
`ActiveDefaultControl`	public	Specifies the active default control on the form.
`AllowDropFiles`	public	Specifies whether files can be dropped onto this form.
`AlphaBlend`	public	Allows the form to be drawn with translucency.
`AlphaBlendValue`	public	The translucence level for the form (0=transparent, 255=opaque).
`AutoScroll`	public	Indicates if the form can automatically show or hide scroll bars.
`BorderIcons`	public	Specifies the icons which appear in the title bar for the form.
`BorderStyle`	public	The border style affects the title bar, border, icon(s), and resize behavior for the form.
`CancelControl`	public	The control associated with the Cancel action.
`Caption`	public	The text displayed in the title bar for the form.
`Color`	public	The background color for the form.
`DefaultControl`	public	The control associated with the default action for this form.
`DefaultMonitor`	public	The monitor on which the form is displayed.
`Designer`	public	The designer object when the form is in design mode.
`EffectiveShowInTaskBar`	public	Value for the ShowInTaskBar property when resolved using the Application settings.
`FormState`	public	State flags for the form.
`FormStyle`	public	Indicates the style for the form.
`HelpFile`	public	The name of the help file for the form.
`Icon`	public	The Icon associated with this Form (in minimized state).
`KeyPreview`	public	Allows the form to intercept keystrokes in child controls.
`MDIChildren`	public	Provides indexed access to MDI child forms when used as a MDI form.
`Menu`	public	The main menu for the form instance.
`ModalResult`	public	Specifies the return value for a form (or dialog) displayed modally.
`Monitor`	public	Returns the Monitor where the form is shown.
`LastActiveControl`	public	Tracks focus changes for the active form or the last active control on the current form.
`PopupMode`	public	Defines where pop-up menus are shown.
`PopupParent`	public	Parent form which owns the current form instance when displayed as a pop-up window.
`SnapOptions`	public	Contains the form and screen snapping options for the form instance.
`ScreenSnap`	public	Indicates whether the form instance can be snapped to an edge on the monitor.
`SnapBuffer`	public	Distance from (or proximity to) an edge on a snap target where the snapping behavior is automatically engaged.
`ParentFont`	public	Uses the font from the Parent when enabled.
`Position`	public	The initial placement for the form.
`RestoredLeft`	public	The Left coordinate for the form when it is restored (i.e. changes from minimized or maximized).
`RestoredTop`	public	The Top coordinate for the form when it is restored (i.e. changes from minimized or maximized).
`RestoredWidth`	public	The width of the form when it is resized.
`RestoredHeight`	public	The height of the form when it is resized.
`ShowInTaskBar`	public	Indicates if the form should be displayed on the system Task Bar.
`TileMode`	public	Controls the layout order for MDI child forms for a MDI form instance.
`Visible`	public	Indicates if the control is visible on its parent.
`WindowState`	public	Indicates whether the form is displayed in a minimized, maximized, full-screen or normal state.

Methods

`WMActivate`	protected	Handles the LM_ACTIVATE message which activates or deactivates the form.
`WMCloseQuery`	protected	Handles the LM_CLOSEQUERY message used to close the window.
`WMHelp`	protected	Handles the LM_HELP window message for the form.
`WMShowWindow`	protected	Handles the LM_SHOWWINDOW window message for the form.
`WMSize`	protected	Handles the LM_SIZE window message for the form.
`WMWindowPosChanging`	protected	Notifies the magnetic window manager when the position for a form is being updated.
`WMWindowPosChanged`	protected	Handles the LM_WINDOWPOSCHANGED window message for the form.
`CMBiDiModeChanged`	protected	Handles the CM_BIDIMODECHANGED control message for the form.
`CMParentBiDiModeChanged`	protected	Handles the CM_PARENTBIDIMODECHANGED control message for the form.
`CMAppShowBtnGlyphChanged`	protected	Handles the CM_APPSHOWBTNGLYPHCHANGED control message for the form.
`CMAppShowMenuGlyphChanged`	protected	Handles the CM_APPSHOWMENUGLYPHCHANGED control message for the form.
`CMIconChanged`	protected	Handles the CM_ICONCHANGED control message for the form.
`CMRelease`	protected	Handles the CM_RELEASE control message for the form.
`CMActivate`	protected	Handles the CM_ACTIVATE control message for the form.
`CMDeactivate`	protected	Handles the CM_DEACTIVATE control message for the form.
`CMShowingChanged`	protected	Handles the CM_SHOWINGCHANGED control message for the form.
`WMDPIChanged`	protected	Handles the LM_DPICHANGED window message for the form.
`WSRegisterClass`	protected	Registers this component class with the current WidgetSet.
`DoShowWindow`	protected	Chooses the active control when the form becomes visible at run-time.
`Activate`	protected	Signals the OnActivate event handler when a form is focused in an application.
`ActiveChanged`	protected	An empty implementation in TCustomForm.
`AdjustClientRect`	protected	Excludes borders from the given rectangle.
`BeginFormUpdate`	protected	Increments the form update counter, and disables auto-sizing on the initial update lock.
`ColorIsStored`	protected	Implements the storage specifier for the Color property.
`CreateParams`	protected	Initializes parameters used to create the handle for the form instance.
`CreateWnd`	protected	Creates the handle for the widgetset class and updates it Menu and Icons.
`Deactivate`	protected	Performs actions when the form loses focus.
`DoClose`	protected	Notifies handlers of the close action for the form.
`DoCreate`	protected	Notifies the create handlers for the form instance.
`DoDestroy`	protected	Signals the OnDestroy event handler for the form instance.
`DoHide`	protected	Signals the OnHide event handler for the form instance.
`DoShow`	protected	Signals the OnShow event handler when needed.
`EndFormUpdate`	protected	Decrements the form update counter, and re-enables auto-sizing on the form.
`HandleCreateException`	protected	Indicates if an exception in the OnCreate event handler is handled by the application.
`HandleDestroyException`	protected	Placeholder for exception handlers in derived classes.
`HandleShowHideException`	protected	Placeholder for exception handlers in derived classes.
`InitializeWnd`	protected	Initializes the widget, also for AlphaBlend and AllowDropFiles.
`Loaded`	protected	Performs actions when the component has been loaded using the LCL streaming mechanism.
`ChildHandlesCreated`	protected	Called when handles for child control are created in the form instance.
`Notification`	protected	Handles the notification when a component is added to or removed from the form.
`PaintWindow`	protected	Calls the Paint method using the specified device context in the control Canvas.
`RequestAlign`	protected	Calls the user Alignment handler (AlignControls). Here: NOP for a top-level form.
`Resizing`	protected	Performs actions needed when the form processes the WMSize message.
`CalculatePreferredSize`	protected	Calculates the clipping width and height for a top-level form on the monitor WorkArea.
`DoOnResize`	protected	Performs a delayed resize action using the DelayedEvent for the control.
`DoOnChangeBounds`	protected	Performs a delayed bounds change using the DelayedEvent for the control.
`SetZOrder`	protected	Moves a top-level form in front of or behind all other forms.
`SetParent`	protected	Sets the value for the Parent property.
`MoveToDefaultPosition`	protected	Moves the form to the location specified in the Position property.
`UpdateShowing`	protected	Configures and position the form when its visibility has been changed.
`SetVisible`	protected	Sets the value for the Visible property.
`AllAutoSized`	protected	If the form is about to show, calculate its metrics.
`DoFirstShow`	protected	Executes handlers using the FirstShow handler type.
`UpdateWindowState`	protected	UpdateWindowState is an empty implementation in TCustomForm.
`VisibleChanging`	protected	Notifies all VisibleChanging handlers.
`VisibleChanged`	protected	Notifies all handlers when the visibility for the form has been changed.
`WndProc`	protected	The general message handler for this control.
`VisibleIsStored`	protected	Implements the storage specifier for the Visible property.
`DoAutoSize`	protected	For internal use only; call AdjustSize instead.
`SetAutoSize`	protected	Sets the value for the AutoSize property.
`SetAutoScroll`	protected	Sets the value for the AutoScroll property.
`SetScaled`	protected	Sets the value for the Scaled property.
`ConstrainedResize`	protected	Signals the OnConstrainedResize handler.
`DoAddActionList`	protected	Adds the specified list of actions to the ActionList for the form.
`DoRemoveActionList`	protected	Removes the specified list of actions from the internal list.
`ProcessResource`	protected	Loads resources needed for the form.
`BeginAutoDrag`	protected	Re-implements the auto-drag behavior for forms.
`DoDock`	protected	Docks or undocks the form in the specified dock site.
`GetFloating`	protected	Gets the value for the Floating properties.
`GetDefaultDockCaption`	protected	Default caption displayed when the form is docked.
`CMActionExecute`	protected	Handles the CM_ACTIONEXECUTE control message.
`CMActionUpdate`	protected	Handles the CM_ACTIONUPDATE control message.
`DoExecuteAction`	protected	Asks all applicable components to execute an action.
`DoUpdateAction`	protected	Tries all applicable components to update an action.
`UpdateActions`	protected	Asks all components on the form to update their actions.
`Create`	public	Constructor for the class instance.
`CreateNew`	public	Creates a form instance without a resource (.lfm) file.
`Destroy`	public	Destructor for the class instance.
`AfterConstruction`	public	Performs actions when the form has been created and loaded from its resource file.
`BeforeDestruction`	public	Performs actions before the form instance is physically freed.
`GetControlClassDefaultSize`	public	Returns the default dimensions for new instances of the class.
`BigIconHandle`	public	Returns the handle for the large icon on the form or in the application.
`Close`	public	Closes the form.
`CloseQuery`	public	Asks the OnCloseQuery handler whether the form can be closed.
`DefocusControl`	public	Updates ActiveControl if it is to be de-focused.
`DestroyWnd`	public	Destroys the interface object (widget).
`EnsureVisible`	public	Ensures that the form is fully visible, and optionally brings it in front of all other forms.
`FocusControl`	public	Gives focus to the specified control.
`FormIsUpdating`	public	Indicates if the BeginFormUpdate method has been called without a corresponding EndFormUpdate method call.
`GetFormImage`	public	Gets the display content for the form as an image.
`GetRolesForControl`	public	Gets the role(s) for the control in a modal form (default or cancel button).
`GetRealPopupParent`	public	Gets the form that is the effective parent for the pop-up, dialog, or splash screen.
`Hide`	public	Hides the control by setting the Visible property to False.
`IntfDropFiles`	public	Invokes the OnDropFiles handler of the form. This function is called by the LCL interface.
`IntfHelp`	public	Shows help for a control or menu item. This function is called by the LCL interface.
`IsShortcut`	public	Determines whether the specified message contains a shortcut or accelerator key.
`MakeFullyVisible`	public	Resizes the form for the specified monitor.
`AutoSizeDelayedHandle`	public	Returns True if an auto-size action should be skipped when a form handle is not available.
`GetPreferredSize`	public	Returns default/preferred height and width, for use in auto-sizing.
`Release`	public	Marks the form for destruction.
`CanFocus`	public	True when the form can receive focus.
`SetFocus`	public	Ensures that the control or window handle has focus.
`SetFocusedControl`	public	Handles a focus change for a control (enter/exit messages).
`SetRestoredBounds`	public	Sets the bounds for the restored control.
`Show`	public	Displays the form instance with support for High DPI scaling.
`ShowModal`	public	Displays the form as a modal dialog.
`ShowOnTop`	public	Displays the form in front of all other forms.
`SmallIconHandle`	public	Returns (and optionally creates) the Handle for the small Icon used for the form.
`GetChildren`	public	Executes the specified callback for all child Controls, and Components with no Parent.
`WantChildKey`	public	Indicates if key messages in a child control are handled in the message processing loop for the form.
`RemoveAllHandlersOfObject`	public	Override this method to remove all references to notification handlers in AnObject.
`AddHandlerFirstShow`	public	Adds a handler routine called the first time the form is shown.
`RemoveHandlerFirstShow`	public	Removes the handler called the first time the form executes its Show method.
`AddHandlerClose`	public	Adds a handler for a form close event.
`RemoveHandlerClose`	public	Removes a form close handler added to the form instance.
`AddHandlerCreate`	public	Adds a handler for a form create event.
`RemoveHandlerCreate`	public	Removes a form create handler added to the form instance.
`ActiveMDIChild`	public	Returns the currently active MDI child form.
`GetMDIChildren`	public	Provides indexed access to MDI child forms when used as a MDI form.
`MDIChildCount`	public	Provides indexed access to MDI child forms when used as a MDI form.
`AutoScale`	public	Sets scaled to True and calls AutoAdjustLayout with the current PPI for the monitor.
`Dock`	public	Docks the form to the specified dock site.
`UpdateDockCaption`	public	Gets the combined Caption for DockClients on the form.

Events

`OnActivate`	public	Handler signalled when the form instance receives focus.
`OnClose`	public	Handler called when the form is closed. It determines what happens to the form (destroy, hide, etc.).
`OnCloseQuery`	public	Event handler signalled when trying to close a form.
`OnCreate`	public	Handler called when the form has been created.
`OnDeactivate`	public	Handler signalled when the form is deactivated (loses focus).
`OnDestroy`	public	Handler called when the form is destroyed.
`OnDropFiles`	public	Handler called when files have been dropped.
`OnHelp`	public	Handler called when Help is requested.
`OnHide`	public	Handler called when the form is being hidden.
`OnResize`	public	Event handler signalled when the size for the form is changed.
`OnShortcut`	public	Event handler signalled when a key is pressed, before further handling of the key.
`OnShow`	public	Handler called when the form becomes visible.
`OnShowModalFinished`	public	Event handler signalled when modal display of the form has been completed.
`OnWindowStateChange`	public	Handler called when the form is minimized, maximized or restored.

Fields

`FActionLists`	protected	Member used to store the action lists associated with the form.
`FFormBorderStyle`	protected	The border style affects the title bar, border, icon(s), and resize behavior for the form.
`FFormState`	protected	State flags for the form.